1. Field of the Invention
The present invention relates to a digital audio tone evaluating system, and particularly to a digital audio tone evaluating system which can objectively evaluate auditory tone quality.
2. Description of the Background Art
Tone evaluation as to digital audio system has heretofore been conducted on a medium in which a digital signal related to voice and/or music has been recorded, as well as a reproducing device for reproducing a digital signal recorded in a medium.
With respect to the medium, a digital signal recorded in a medium to be evaluated is reproduced by a standard reproducing device having a required performance, and the reproduced digital signal is analyzed, thereby conducting the evaluation of the medium. On the other hand, concerning the reproducing device, a prescribed digital signal recorded in a standard medium is reproduced by a reproducing device to be evaluated, and the reproduced digital signal is analyzed, thereby conducting the evaluation of the reproducing device. In the analysis of each digital signal, the reproduced digital signal related to voice and/or music is generally subjected to signal processing by fast Fourier transformation (FFT), thereby obtaining data related to frequency characteristics. This data is compared with the reference data from, for example, a master tape.
The fast Fourier transformation is a method for operating representation (Fourier transformation) in a frequency domain to a waveform (period function) in a time domain at a high speed, and is representative of frequency spectrum analysis.
Various waveforms forming voice and music generally contain a great number of frequency components. When a continuous-time signal f(t) by these waveforms has a constant period T, namely, f(t)=f(txe2x88x92T), the continuous-time signal f(t) is expressed by the following equation (1):       f    ⁡          (      t      )        =            ∑              n        =                  -          ∞                    ∞        ⁢                  C        n            ⁢              ϵ                  j          ⁢                      xe2x80x83                    ⁢          n          ⁢                      xe2x80x83                    ⁢          ω          ⁢                      xe2x80x83                    ⁢          t                    
wherein xcfx89 is an angular frequency (2xcfx80/T), and Cn is a higher harmonic amplitude represented by the following equation:       C    n    =            1      T        ⁢                  ∫        0        T            ⁢                        f          ⁡                      (            t            )                          ⁢                  ϵ                                    -              j                        ⁢                          xe2x80x83                        ⁢            n            ⁢                          xe2x80x83                        ⁢            ω            ⁢                          xe2x80x83                        ⁢            t                          ⁢                  xe2x80x83                ⁢                  ⅆ          t                    
Such a continuous-time signal is sampled at fixed time intervals, and the discrete Fourier transformation (DFT) of the sampled signals is operated at a high speed, thereby obtaining the fast Fourier transformation. Accordingly, the resolution of frequency by the fast Fourier transformation comes to the division of the specified frequency band by a constant frequency width, and the time resolution also becomes constant.
However, the analysis of a digital signal by the fast Fourier transformation is used with the principal object of observing frequency characteristics and does not represent human auditory characteristics themselves having peculiar time constitution and frequency resolving power.
There are also means for evaluating frequency characteristics through an equalizer having auditory correction characteristics that change a level according to frequency in imitation of the sense of hearing. However, such characteristics are different from actual auditory characteristics and correspond thereto only when a reproduced sound is lower than a certain level, and so they are strictly only data not much exceeding reference. Therefore, such means are not practical.
In recent years, it has been pointed out that when sounds reproduced by digital audio are auditioned, their tone qualities delicately vary according to the materials of media or reproducing devices though no difference is observed in analyses by the fast Fourier transformation. However, such tone evaluation is subjective evaluation by listeners, and there has not been yet conducted under the circumstances any objective tone evaluation according to the human sense of hearing.
The present invention has been made on the basis of the foregoing circumstances and has as its object the provision of a digital audio tone evaluating system which can objectively evaluate auditory tone quality by digital audio.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided a digital audio tone evaluating system comprising an analyzer for subjecting a digital signal related to voice and/or music to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the present invention, there is also provided a digital audio tone evaluating system comprising:
a reproducing device for reproducing a digital signal according to a specified digital audio format, related to voice and/or music recorded in a medium to be evaluated; and
an analyzer for subjecting the digital signal from the reproducing device to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the present invention, there is provided a digital audio tone evaluating system comprising:
an analyzer for subjecting a digital signal, which is inputted from a reproducing device to be evaluated for producing a digital signal according to a specified digital audio format, related to voice and/or music recorded in a standard medium, to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the present invention, there is further provided a digital audio tone evaluating system comprising:
a reproducing device for reproducing a digital signal related to voice and/or music recorded in a medium to be evaluated;
a digital-analog converter for converting the digital signal from the reproducing device into an analog signal;
an analog-digital converter for converting the analog signal from the digital-analog converter into a digital signal according to a specified digital audio format; and
an analyzer for subjecting the digital signal from the analog-digital converter to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the present invention, there is still further provided a digital audio tone evaluating system comprising:
a digital-analog converter for converting a digital signal, which has been outputted from a reproducing device to be evaluated by which a digital signal related to voice and/or music recorded in a standard medium is reproduced, into an analog signal;
an analog-digital converter for converting the analog signal from the digital-analog converter into a digital signal according to a specified digital audio format; and
an analyzer for subjecting the digital signal from the analog-digital converter to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the present invention, there is yet still further provided a digital audio tone evaluating system for evaluating a digital-analog converter built-in reproducing device, comprising:
an analog-digital converter for converting an analog signal, which has been outputted from a reproducing device to be evaluated by which a digital signal related to voice and/or music recorded in a standard medium is reproduced and converted into the analog signal, into a digital signal according to a specified digital audio format; and
an analyzer for subjecting the digital signal from the analog-digital converter to signal processing, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form.
According to the digital audio tone evaluating systems of the present invention, a digital signal related to voice and/or music is subjected to signal processing in the analyzer, thereby operating a factor which expresses the auditory tone quality of the voice and/or the music by the digital signal in a digitized form. Therefore, the auditory tone quality can be objectively evaluated without actually auditioning the voice and/or the music.
In addition, a digital signal from a reproducing device is converted by the digital-analog converter into an analog signal, and the analog signal from the digital-analog converter is converted by the analog-digital converter into a digital signal according to a specified digital audio format which can be processed by the analyzer, and so tone evaluation can be conducted as to media in which digital signals according to various digital audio formats have been separately recorded, and reproducing devices for reproducing the digital signals in these media, by use of the analyzer commonly.